This study examines whether semantic relatedness facilitates or impedes the acquisition of English collocations by conducting two experiments respectively on Chinese undergraduates. Each experiment was composed of a reading session, a productive test, and a receptive test. Experiment 1 began with the reading session of 28 paired-up words and their collocations (in sentence context). Those words were counterbalanced between two randomly selected groups by cross-matching on semantic relatedness. Results of the productive test revealed that the participants scored significantly higher on test items that were semantically related than the randomly cross-paired counterparts. However, for the receptive test, the participants performed significantly better on semantically unrelated items. Experiment 2 was similar to Experiment 1 except that the word pairs selected were only semantically related and did not have any shared morphemes. Experiment 2 also revealed consistent results. The results of the two experiments consistently illustrate that semantic relatedness may exert a facilitatory effect on language output but an inhibitory effect on the process of language input.